The cost of printing cookbooks is $2.09 per book plus a one time setup fee of $349. all taxes are included. which of the following functions models a(x) the average cost per book of printing x books

For this case we have the following variable:
 x = number of books
 We write a function of the form:
 y = mx + b
 Where,
 m = 2.09 $ / book
 b = 349 $
 Substituting values:
 a (x) = 2.09x + 349
 
 A function that models a (x) the average cost per book of printing x books is:
 a (x) = 2.09x + 349

What do you think the answer is?